Electroless plating is a well documented process which has evolved into a mature science with many commercial applications. During the last forty years hundreds of patents were issued and texts published describing the various improvements to this basic autocatalytic phenomenon in which metals and alloys can be deposited without the use of an external power supply. Electroless plating can be used for the deposition of many metals, including but not limited to: nickel, cobalt, copper, precious metals and various alloys such as tin-lead, and others. Perhaps one of the more recent texts entitled "Electroless Plating Fundamentals and Applications" edited by G. Mallory and J. Hadju, published by The American Electroplaters and Surface Finishers Society, Inc., Orlando, Fla., 1990, describes the state of the art in conventional electroless plating of the various metals and alloys-including typical formulations and performance. In the typical electroless plating formulation there are certain key components which are common from bath to bath. These key components can be described as: 1) a metal salt as a source for the metal ions; 2) an electroless reducing agent which provides through interaction with the surface the reducing capability of the surface; 3) a complexing agent and/or chelating agent to complex and tie the metal ions and thereby insure their stability and; 4) stabilizers which are added to insure that no homogeneous decomposition takes place and that the chemical reduction of the metal ion be limited to the surface of the substrate only. In many of the electroless formulations, a wide variety of reducing agents have been reported ranging from sodium hypophosphite, formaldehyde, hydrazine, and amine-borane, and its derivatives. Much of the successful commercial developments of electroless technology has relied upon the utilization of stabilizers. Though there are many stabilizers reported in the literature, some of the more effective stabilizers belong to the following classes.
I. Compounds of group VI elements, i.e., sulfur, selenium, tellurium and others. PA1 II. Compounds containing oxygen, i.e., arsenite, bromate, iodate, molybade and tungstate and others. PA1 III. Heavy metal ions, i.e., Lead, mercury, thalium, tin, cadmium and others. PA1 IV. Unsaturated organic compounds: maleic, itaconic and others.
The presence of the stabilizer(s) and its concentration(s) is particularly critical for it has been noted that excess addition may create a complete cessation of the plating process. In fact, monitoring the plating rate or the mixed potential developed vs. the stabilizer concentration generally provides a curve similar to titrations in analytical chemistry. Exceeding a critical concentration will create cessation of the plating. This phenomenon has been reported by N. Feldstein and P. Amadio, Jr. ElectroChem. Society, 117, 1110, (1970) and is also described in the above text at page 36 and 37. As was noted above, some of the stabilizers used though highly effective, are highly undesirable. For instance, the use of thallium is undesirable. The use of mercury is also highly undesirable. The use of lead is undesirable in certain applications, e.g., food industry. Consequently, there is a continuous need for a new type of stabilizer which will not be poisonous and potentially hazardous when trapped in the coating or adversely affect the environment.
It has now been discovered that the use of a cobaltic type product provides the characteristics associated with typical stabilizers. Consequently, the adaptation of this new class of stabilizer will open up new avenues for processes and compositions for electroless plating of the various metals and alloys with a metallic ion which is not poisonous or detrimental when incorporated into the coating and used in food applications and others.